Explosion-proof lighting unit



Jan. 18, 1944. E. H. BENsoN 2,339,670

EXPLOSION-PROOF LIGTING UNIT File-d May 21. 1942 v with tools or. machinery.

Patented Jan. 18, 1944 UNITED STATES naar ATENT omer.

ExPLosmN-rnoolr LIGHTING UNrr Application May 21', 1942, Serial No. 443,861 (C1. zio- 112)` 2 Claims.

My invention relatesto afnovel construction of an explosion-proof lighting .unit-and relates more particularly to a construction whichprovides a strong, rugged unit and one in which the parts are so assembled as to form a pressure-y tight unit.

In factories. and manufacturing plants frequently the atmosphere contains explosive vapors. Under such conditions, the lighting units must be protected as failureor breakingv ofa heated bulb may ignite the vapors resulting in an explosion or `re. Theusual practice has l.been to enclose the bulb in a housing` which has a thick lens through which the light .is to be projected. Such a, unitmust have vapor-tightjoints to preventexplosive vapors from entering, the hous- Itis further desirablev and necessary to have the unit rugged iniorder to withstandabusesinceY workmen oftentimes` inadvertently strikethe unit It is also important that such a unit belight in weight since itis sometimessuspended on a lexiblecord and used:

as adlOp light.

There are definite specicationsstipulated .by the Fire Underwriters requiring that light units;

of thischaracterpass certain rigid tests. For instance, the housing must withstand 500 pounds per square inch hydraulic pressure without rupture or failure of the joints. Small units utilizing relatively low candle power can be built to withstand this pressure but, to my knowledge, no satisfactory unit of a thousand-watt capacity has been produced. Standard modes of construction used in smaller capacity lighting units have failed to meet the rigid requirements imposed.

The salient object of my invention is to provide a large size, explosion-proof lighting unit that is sufficiently rugged to pass the required tests.

In brief, my invention comprises a housing for a high capacity light bulb having a thick, tough pressure-resistant transparent lens removably held in an opening in the housing by pressure gripping elements.

In the drawing forming a part of this specication and wherein like numerals are employed to designate like parts throughout the same,

Fig. 1 is a front elevation of an explosionproof lighting unit embodying my invention, parts being broken away for clearness of illustration,

Fig. 2 is a fragmentary bottom plan view of the unit.

at least a thousand watts. The housing, prefer-- ably made of aluminum or .alloys of aluminum or magnesium is generally bell-.shaped tovconformr with the shape of the light bulb and t0 provide.

ample space between the housing and bulb. Vertical iins lila are provided on the outer surface of housing I0 to dissipateheat created by the bulb l l; For mounting the bulb II within the housing I provide a socketv I2 into which the bulb-is threaded. The socket l2 is suspended within the housing I0 by a bracket; A junction box i4 threaded on the reduced upper end of housingY lil retains an insulating block l5.

Screwed into the upper end of thejunction box ,l 4,

isa pipe :I6 which hangs vfrom the ceiling and froms `a ,conduit for electrical conductors ll and la. The ends of conductors Il and I8 connect with terminals illand Zil'carried` by an insulating bar 2l,'secured to support lfla integral'with junction box I4. A removal plug 22 in the junction box permits easy access to the terminals i9 and 29. Suitable conductors 23 and 24 connect terminals I9 and 20 with the light bulb ll.

Into an opening in the lower end of housing Il) and abutting shoulder Ic is screwed a soflit ring 25. A tool may be inserted through an opening llb in housing I to engage gear teeth 25a on the soft ring for tightening the ring. A Spanner wrench may also be used against lugs `25h on the bottom of the sofflt ring to tighten or loosen the same.

A heavy rugged transparent lens of glass, quartz or transparent plastic 26 lits within the soit ring and is supported by a radial ange 25e.

Filling the annular space between the lens 26v and somt ring 25 is a relatively soft metal rim 27 of solder, lead, babbt, white metalvalloys or the like. The soft metal of rim 2l forms a buffer a groove in the soft ring and edges of the rim.

overlap beveled edges of the lens to securely retain the lens within the rim and solt ring. A sphero-parabola reiiector 28 supported within the housing by brackets 29 surrounds light bulb Il and directs light through lens 26.

The construction employing a soft metal rim on the lens anda sot ring is generally satisfactory for small explosion-proof lighting units; but, when a light source of a thousand-watt capacity is necessary, the housing and lens joint must be designed to withstand the conditions specified. When a conventional aluminum housing of this size is exposed to the required tests, it frequently fails and is inadequate structurally. I have found, however, that if a hard metal holding band 30 is placed exteriorly of the housing in a position to circumscribe and surround the joint between housing I and lens 26, a pressure-tight joint is assured. The holding ring, preferably made of steel, has a diameter which makes a press t with the skirt or rim of the housing. As the holding ring is pressed into place, it exerts a wedging or constricting action upon the housing and the relatively soft materials of the housing, soilt ring and lens rim yield suiciently to assure vapor-tight joints.

A plano-convex fresnel type lens 3l is supported below lens 26 by a spun retainer ring 32. The control lens 3| concentrates the light from bulb 28 and pigment red into the lens eliminates vglare and assures low surface brightness without objectionably reducing the intensity of the light.

A wire lens retainer hanger 33 is attached to the housing to support the lenses 26 and 3| when they are removed for servicing.

In Fig. 5, I show a modified type of lens wherein the transparent lens 26 and control lens 3l shown in Figs. 1 and 3 are formed as a single unit, providing a composite lens 34. The lens 34 is formed thicker than lens 26 in Fig. 1 and the bottom surface thereof is cut to form prisms which control the light rays in the manner of lens 3l.

It may thus be seen that I have accomplished the objects of my invention. The sot ring 25 surrounds and supports lens 26. The joints between the lens and the sot ring and between the soilt ring and the housing are concentrically disposed in the same plane. In the past, the

threaded union between the housing and the soflit ring of large units has opened as a result of a blow or under pressure sufficiently high to disrupt the housing. Since all of the joints that can open to admit vapors into the housing are concentrically disposed in the same plane, I surround the housing with a hard steel holding band which circumscribes the joints. 'I'he holding band must be pressed onto the rim of the housing. The pressure exerted by the band wedges the housing, lens and s'oit ring into a pressure-tight joint.

Actual tests have demonstrated that a unit constructed in this manner is much stronger and more rugged than any unit heretofore developed.

It is to be understood that the forms of my invention herewith shown and described are to be taken as preferred examples of the same and that various changes in the size, shape and arrangement of parts may be resorted to without departing from the spirit of my invention or the scope of the appended claims.

' Having thus described my invention, I claim:

1. In an explosion-proof lighting unit, a housing, a light source in the housing, a rugged trans parent lens iltted into the opening in the housing, a relatively yieldable joint between the lens and housing including a rim bounding the edge of the lens,y 4means including a sot ring for retaining the lens in place in the housing and a holding band exterior of the housing circumscribing the joint between the housing and lens, said band having a press fit with the housing and adapted to wedge the lens,'sofflt ring and rim into f a pressure-tight joint.

2. In an explosion-proof lighting unit of the type including a relatively thin metal housing, a soft ring threaded into th lower end of the housing and a lens retained within the ring by a soft metal, the improvement comprising strengthening the unit without appreciably increasing its weight by means of a rigid holding band exterior of the housing, said band circumscribing the joint between the housing and soft ring and having a pressed t with the housing whereby to compress it sufficiently to render said joint vapor tight.

ERNEST H. BENSON. 

